In recent years there has been considerable effort to provide full color display systems which do not rely upon the conventional color cathode ray tube. The elimination of cathode ray tubes for systems such as television receivers, computer monitors, and the like, has been prompted for many reasons.
Conventional cathode ray tubes are large in size and thus occupy a considerable portion of the cabinetry in which they and their associated circuitry are housed. Also, because thick glass walls are used to form the enclosures of the cathode ray tubes, they are generally quite heavy accounting for an inordinate proportion of the overall weight of a television receiver or monitor. In addition, cathode ray tubes include an elongated neck portion to permit the acceleration of an electron beam from an electron gun to the cathode ray tube faceplate and hence, are irregular in shape.
In addition to the problems posed by the physical characteristics of conventional cathode ray tubes, the electrical requirements of conventional cathode ray tubes can also pose problems. Cathode ray tubes require a high voltage power supply to obtain sufficient acceleration of the electron beam to sustain the operation of the cathode ray tubes. Such power supplies can require transformers and other circuit components which add to the weight and size of the systems in which they are employed. The high voltage also creates an obvious safety hazard. In addition, compensating components are required to correct for nonlinear operation of the tubes and shielding is also required to prevent external magnetic fields from adversely effecting the desired path of the electron beam. Without such compensating and shielding components, distorted images would result.
While cathode ray tubes have changed very little over the years in terms of their physical characteristics and electrical requirements, there have been significant advances in the area of circuit development. Circuits are now more compact, capable of operating at lower currents, and hence are more portable than ever before. In short, cathode ray tubes have fallen out of step with circuit development due to their lack of portability and flexibility of application.
One system which has been proposed to eliminate the color cathode ray tube includes a back illuminated liquid crystal display having a plurality of pixels arranged in plural groups of three pixels. Each pixel of each group includes a color filter of a respective one of the primary colors, such as, for example, red, green, and blue. The pixels of each color are scanned together such that all of the red pixels are scanned, all of the green pixels are scanned, and all of the blue pixels are scanned simultaneously. The red, green, and blue pixels are scanned at a fast rate to present full color image fields in sequence for each frame. The frame rate is fast enough so that the human eye can integrate all of the colors and intensities together. As a result, a full color, moving display is obtained.
The system mentioned above suffers from two primary draw backs. Resolution is poor because the color pixels are of finite dimension and three separate color pixels are required to constitute one complete picture element of the display. Also, because pixels are of small dimension and of each primary color must be integrated together, the processing for making the display is extremely difficult.
Other systems have been proposed but each has not found commercial acceptance. These systems suffer from lack of resolution, lack of brightness, or are too complex to represent a sufficient economic advantage over the conventional color cathode ray tube.